Browser script, DOM, control HTML attributes

Hi, siebel experts.
Can somebody provide any example, how to use control property: "HTML Attributes"?
I added "Id=Test" to that property, and trying to access this control in browser script by DOM: document.getElementById("Test"), but i always getting "null" value. Control html type - MiniButton
Thanks in advance

try these commands and you will understand onkeyUp="if(/[^0-9]/.test(this.value) ){ alert('The License Number field accepts only numeric data.'); this.value='';}" onBlur="if(/[^0-9]/.test(this.value) ){ alert('The License Number field accepts only numeric data.'); this.value='';}"

In addition to numeric validation, I also want to check the field length for 15 digits. so Can i write onBlur="if(this.length <> 15 ){ alert('License Number can be only 15 digits.'); this.value='';}" I tried giving this in HTML attrib but it is not working. Please suggest. Thanks, Nitin Prasad